Method of treating cellulosic solutions



Patented Aug. 13, 1935 UNITED. STATES METHOD OF TREATING CELLULOSICsotUTIoNs Robert W. Maxwell, Wilmington, DeL, assignor to Du Pont RayonCompany, New York, N.,Y., a corporation of, Delaware t i No Drawing.Application Apri1a'19s4, r 7 Serial No. 7183877 Y "aoc aims. (01. 106-40tThis invention relates tothe' treatment of cele lulosic solutions, and,in particular, itpertains to amethod for controlling the degreeofripening of viscose.

5 'r- In the-manufacture of'filaments, wrapping tissues and otherarticles from viscose, it is essential for'successful commercialoperation to control the degree of ripening of viscose so as to produce,after coagulation and regeneration, filaments, sheets. and the like,having satisfactory physical characteristics. h ---,Ihe, rate ofripening of viscose is quite rapid, and unless properly allowed for orcontrolled, causes great difficulty in producing products hav ingiuniform and otherwise satisfactory physical characteristics. Thus, byway of example, in the production of artificial threads, viscose isintroduced. into and is passed through the spinning room through a. longseries of pipes, and ordiu narily will pass through more pipe in beingdelivered to one spinning machine than to another. In addition, afterbeing delivered to a spinning machine, the viscose will 'have adifferent length of travel for'the different spinnerettes, e. g.,' theviscose delivered to the spinnerettes at one end of the spinning machinemay travel farther than that delivered to the spinnerettes at the otherend of the machine. The viscose necessarily travels at a rather slowrate of speed through the pipes, and its temperature in passing throughthe spinning room is moderately high. Both of these factors increase thedegree of ripening of the viscose.- f

The art has long been concerned "with this problem and a large number ofmate-rials have been suggested for use as inhibitors to control viscoseripening. Of the materials suggested for .useas inhibitors, only a smallnumber, to wit, sodium sulfite, and/to a lesser degree, sodium.arsenitejha've shown promise. One object of the invention pertains toan emcient method for controlling viscose ripening. Another object ofthe invention comprises a method for slowing down the" normal rate ofviscose ripening. A further object relates to the substantial inhibitionof viscose ripening. :A further object of the inventionis concerned withthe inhibition of the ripening of viscose during its conduction to theforming devices. Other objects of theinvention will appear hereinafter.

It hasbeenfound in accordancewith the presentinventionthat water-solublecyanides and, particularly, alkali metal cyanides, can be used in verysmall amounts to successfully control or inhibit the 'ri'pening ofviscose. The following examples which are intended to be illustrativeonly indicate specific applications of the invention:

Example I.0.25 pounds of sodium cyanide are mixed with 1000 pounds of aviscose containing 7% cellulose and 6% sodium hydroxide just prior tothe introduction of the viscose into the spinning room. The viscoseassumes a pinkish cast almost immediately and the rate of ripening isreduced two-thirds as measured by the rate of change in the salt index.

\ Example II.This is the same asExample I except that'the same amount ofsodium cyanide is added in the form of a 7% aqueous solution. The rateof viscose ripening is reduced very substantially as in Example I.

Example III .'-To. 1000 pounds of partially mixed viscose inthe mixer isadded 0.5 pounds of potassium cyanide. If desired, the cyanide can beaddedin the mixing caustic solution. The resultingviscoseripens at aboutone-third the usual rate as 'measured by the rate of change in saltindex. p

Example IVA-This." example is the same as Example III. except that 0.25pounds of hydrocyanic acid is added in-plac'e of the potassium cyanide;A substantialdecrease in the rate of viscose ripening occurs. i

Although I do not wish to be limited to theory, the inhibiting effect ofthe alkali cyanides is believedito bedue 'to the fact that they reactwith persulfi'des (which have an accelerating effect on the ripening ofviscose and which are present in normal viscose) to'form thiocyanate andthe corresponding sulfide. As a general rule, the alkali metal cyanidesneed. be added only in that quantity necessary to. destroy thepersulfide. This amount will vary depending upon the particular type ofviscose to be treated, the use to which the viscoseis to be put, i. e.,whether it is to be used to make sheets or filaments, and thatpoint ofripening at which the inhibitor is incorporated in the viscose. Theamount of inhibitor used may, for example, be varied between 0.1% orlower up to 2% or higher, based on the cellulose content of theviscose.In the ordinary commercial viscose used in the spinning of rayonfilaments, and where the inhibitor is introduced in the viscose when ithas reached that state of ripening at which it is to be spun, i. e.,atthe spinning index, 0.35% sodium cyanide, based on the cellulose contentof the viscose, is suificient to reduce the rate of ripening to aboutone-third of its original value.

In its preferred form, the invention comprehends the treatment ofviscose which is to be spun into filaments. -Without the use of aninhibitor, it is extremely difficult to deliver to all of thespinnerettes viscoseof a uniform degree of ripeness, since the viscose,in travelling through the spinhing room at a'moderately hightemperature, continues to ripen at a fairly rapid rate in the pipes andis delivered to the different spinnerettes at difierent degrees ofripeness. When, however, a cyanide inhibitor is added to the viscose atthat point of ripeness at which the viscose is ready to persulfides. Theamount of inhibitor necessary to obtain the desired eiiect can beestablished roughly by determining the quantity necessary to bring outthe pink color.

Temperature has a definite effect on the action of the cyanide 7inhibitor. Thus, where ripening of the 'viscosetakes place at about 18C., the effect of the inhibitor over the life of the viscose isapproximately the same, whether the inhibitor is added during the mixingof the viscose or at a point close to the spinning index. Where theripening takes place at higher temperatures, for instance, at about 300., the inhibitor tends todiminish in efficiency after a short time. Forthis reason, when the inhibitor is introduced into viscose attemperatures of the order of 30 C. or higher, the addition is preferablydelayed until just before coagulation and/ or regeneration of theviscose. Where the inhibitor is introduced at some prior point, moreinhibitor may be added over and above that which is sufficient when itis introduced just prior to coagulation and/or regeneration of theviscose.

The inhibitor can be added either in solution or as a solid, and it maybe added to the viscose at the spinning index or in the mixer; asillustrated in Example IV, the cyanide inhibitor may be formed in theviscose by the introduction therein of hydrocyanic acid, therebyyielding sodium cyanide.

The use of cyanides as inhibitors of viscose ripening may be usedwherever viscose is used, e. g., in the production of artificial thread,wrapping tissue, bottle caps and bands, artificial sponges, or othermolded or cast articles. The inhibitor may be added at any point duringthe ripening of the viscose, depending on the degree of ripeningdesired.

In its broadest scope, the invention comprises the use of water-solublecyanides as inhibitors of viscose ripening. The alkali metal cyanideshave been found to be particularly efiicient. For the purposesof thisinvention, ammonium cyanide is intended to be included as an alkalimetal cyanide.

Percentages referred to throughout the specification are percentages byweight.

Any variation or modification of the process as describedin the abovespecification and examples, which conforms to the spirit of theinvention, is intended .to be included within the scope of the claims.

I claimi 1. A composition of matter comprising viscose which contains awater-soluble cyanide containing the negative radica1(CN-).

2. A composition of matter comprising viscose which contains an alkalimetal cyanide containing the negative radical-(CN-).

3. A composition of matter comprising viscose which contains sodiumcyanide.

4. A composition of matter comprising partially ripened viscose whichcontains a watersoluble cyanide containing the negative radical- 5. Acomposition of matter comprising partially ripened Viscose whichcontains an alkali metal cyanide containing the negative radical (CN-)6. A composition of matter comprising partially ripened viscose whichcontains sodium cyanide.

The process which comprises adding to viscose a water-soluble cyanidecontaining the negative radical(CN) 8. The process which comprisesadding to viscose an alkali metal cyanide containing the negativeradical(CN-)'.

9. The process which comprises adding to viscose sodium cyanide.

10., The process which comprises adding to viscose a water-solublecyanide in aqueous solution said; cyanide containing the negativeradical-(CN) 11. The process which comprises adding to partiallyripened.- viscose a water-soluble cyanide said cyanide containing thenegative radical-(CN').

1-2. The process which comprises adding to partially ripened viscose analkali metal cyanide said cyanide containing. the negativeradical-KIN").

13. The process which comprises adding to partially ripened viscose,sodium cyanide.

14. The process which comprises introducing a Water-soluble cyanide intoviscose which has been ripened to about the salt index at which it is tobe coagulated said cyanide containing the negative radical(CN-) 15. Theprocess which comprises introducing an alkali metal cyanide into viscosewhich has been ripened to about the salt index at which it is to becoagulated said cyanide containing the negative radical--(CN-) 16. Theprocess which comprises introducing sodium cyanide into viscose whichhas been ripened to about the salt index at which it is to becoagulated.

17.. In the production of regenerated cellulose filaments from viscose,the step which comprises adding a water-soluble cyanide to the viscosejust prior to its introduction into the spinning room saidcyanidecontaining the negative radical- (CN-) 18. In the production ofregenerated cellulose filaments from viscose, the step which comprisesadding an alkali metal cyanide to the viscose just prior to itsintroduction into the spinning room said cyanide containing the negativeradical v(CN 19. In the production of regenerated cellulose filamentsfrom viscose, the step which comprises adding sodiumcyanide to theviscose just prior to its introduction into the spinning room.

20. In the production of regenerated cellulose filaments from viscose,the step which comprises adding sodium cyanide to the Viscose just priorto its introduction into the spinning room, the sodium cyanide beingadded in an amount of about 0.35% by weight, based on the cellulosecontent of the viscose.

ROBERT W. MAXWELL.

